In recent years, development of the Communications-Based Train Control (CBTC) system that does not require a track circuit has progressed. The CBTC system is configured so that an onboard system measures position information about the train, and transmits the position information to a ground system via wireless communication, and the ground system detects the position of the train based on the position information to control the train.
The onboard system detects the train position by measuring the rotational speed of a tacho-generator attached to the axle, for example, and the measured train position contains a measurement error. A technique that utilizes a range obtained by adding a margin distance (train length correction value) to the actual train length when detecting occupancy using the ground system has been proposed (see Japanese Patent No. 4575807, for example).
A technique has been generally used that corrects the train position based on the installation position (absolute position) of a correction coil acquired through communication with the correction coil when the train passes by the correction coil provided along the track in order to reduce a measurement error of the train position measured by the onboard system.
When correcting the train position by utilizing the correction coil, the train position may change (i.e., may be shifted forward/backward) due to correction. The ground system of the CBTC system determines whether or not each block section is occupied by a train based on the train position received from the onboard system. However, a change in train position due to correction may pose a problem when determining whether or not each block section is occupied by a train.
Specifically, when the train position measured by the onboard system precedes the actual train position, the train position is corrected backward when the train has passed by the correction coil. For example, when the rear end of the train that has been present within a second block section that follows a first block section is returned to the first block section due to backward correction, it is determined that the first block section is not occupied before correction, but is occupied after correction. Specifically, the first block section that has been detected to be unoccupied by the train that travels forward is occupied by the train again. In this case, the following train that is entering the first block section must be stopped rapidly since the following train is not allowed to enter the first block section. The above problem also occurs when the train position is corrected forward.